I have two five gallon gas cans purchased new about five years ago. I used them to take to my boat so I didn't pay gas-dock prices. They held 2-cycle mixed gas. If I made sure they were empty, didn't clean them, and then filled with unleaded, would it screw anything up in a four cycle ATV? Assuming there is going to be some residual in the tank. If it would, how does one clean a gas can? Or do I spend the $$$ and just buy new ones.